As a result of global warming, greenhouse gas reduction plans are reported in all the countries of the world, and South Korea government determined the reduction target of greenhouse gas to 30% relative to the observation value of emission in 2020, thereby increasing the burden in industry. Particularly, damages to steel industry, automobile industry, petrochemical industry, etc., which are energy-guzzling industries and leading export industries seem inevitable. However, the energy efficiency level of domestic companies is already the best in the world, and the capacity available for further reduction of greenhouse gas has limitation. If the reduction is conducted by government regulation, the companies may relocate their plants abroad or may experience delay in production.
As an alternative, the focus of the present invention is not the reduction of the emission amount of carbon dioxide, but the recycling for using emitting carbon dioxide. One of various methods for recycling carbon dioxide is preparation of a synthesis gas through reforming methane using carbon dioxide. The reforming method of methane using carbon dioxide has the merits of removing carbon dioxide and methane, which cause global warming at the same time and preparing a synthesis gas including relatively high content of carbon monoxide (H2:CO=1:1) when compared to other reforming methods. Therefore, the synthesis gas thus prepared may be used as a reactant in a producing process of chemical products with high value such as oxoalcohol, dimethyl ether (DME), polycarbonate (PC), and acetic acid.
A carbon dioxide reforming reaction of methane may be performed as the following Reaction 1.CH4+CO2→2CO+2H2,ΔH2980=+247.3 kJ/mol  [Reaction 1]
The reaction is a strongly endothermic reaction. The conversion ratio of equilibrium that is a theoretically maximum conversion ratio at a certain temperature increases according to the increase of the temperature, and the reaction is carried out at the temperature of 650° C. and more. Commonly, the reaction is carried out at the high temperature of 850° C. According to the reaction, since the carbon to hydrogen ratio of reaction gases is high, carbon may be easily produced thermodynamically, and the development of a catalyst restraining the production of cokes and the deactivation due to sintering is required.
In addition, the realization of an appropriate catalyst shape is also significant. In case of using a powder, the application to a process may be difficult due to extreme pressure drop at more than a certain value of flow rate. A catalyst with a granule or pellet shape also may cause pressure drop at a high flow rate. If heat transfer is not smooth, the local temperature in the catalyst may increase largely, and the catalyst may be damaged. In addition, gradual loss of the catalyst may be generated by the abrasion due to mechanical stress.
To solve the above-described limitations, a monolith substrate with a honeycomb structure may be used. In a monolith catalyst in which empty spaces with a rod shape and a honeycomb structure are connected, heat may be easily transferred via walls, and the temperature of the catalyst may be uniform, and the pressure drop may be small. Thus, the monolith catalyst is an appropriate type for treating reactants with a high flow rate. Due to a dense structure, the monolith catalyst has a large surface area per unit volume and excellent abrasion-resistance. By applying the monolith catalyst in a carbon dioxide reforming reaction, low deposition of carbon due to rapid material transfer, durability reinforcement of the catalyst due to high thermal stability, and process compatibilization due to reaction possibility at a high flow rate, may be realized.
Common catalysts for the reforming reaction of methane using carbon dioxide will be explained. Methods for preparing a catalyst by impregnating a nickel metal in magnesium oxide (MgO) and magnesium oxide-alumina (MgO—Al2O3) supports are disclosed in a literature to Fujimoto, et al. [Chemistry Letters, Reduction of carbon dioxide by methane with Ni-on-MgO—CaO containing catalysts, (1992), 1953-1954] and Korean Patent No. 1999-0061517.
In literatures to Verykios, et al. [Catalysis Letters, Mechanistic aspects of carbon dioxide reforming of methane to synthesis gas over Ni catalysts, 38 (1996), 157-179] and [International Journal of Hydrogen Energy, Catalytic dry reforming of natural gas for the production of chemicals and hydrogen, 28 (2003), 1045-1063], a nickel metal is carried in a lanthanum oxide (La2O3) support.
Korean Patent Application No. 1999-0050013 discloses a nickel-based reforming catalyst according to a chemical formula obtained by impregnating a nickel metal together with a co-catalyst including an alkali metal, an alkaline earth metal, etc. in a zirconia support in which ZrO2 is modified with an alkaline earth metal and a metal in IIIB group or lanthanides.
Korean Patent Application No. 1993-0016885 discloses a catalyst obtained by impregnating an alkali metal, an alkaline earth metal co-catalyst and nickel in a silicon-containing support such as zeolite, silica, silicate, and silica-alumina, and Korean Patent Application No. 2008-0073003 discloses a catalyst obtained by impregnating an alkaline metal oxide of calcium and potassium as a co-catalyst in a silica mesopore molecular sieve support.
In such reforming reactions of methane using carbon dioxide, developments on a nickel support catalyst with high performance having strong resistance to carbon deposition at an affordable price as in the reforming reaction of vapor are continuously conducted, however are confronted by limitations due to the short catalyst life of nickel. Meanwhile, studies on noble metal catalysts having higher resistivity on carbon deposition and activity than the nickel-based catalyst, however having high price disadvantages are being actively conducted.
U.S. Pat. No. 5,068,057 discloses Pt/Al2O3 and Pd/Al2O3 catalysts, and PCT Patent Publication No. 92/11,199 suggests that an alumina catalyst impregnating a noble metal such as iridium, rhodium and ruthenium has high activity and long life.
PCT Patent Publication Nos. 2004/103555 and 2008/099847 suggest catalysts including copper as an essential element and at least one element selected from nickel, cobalt and platinum and having a spinel structure as a metal oxide. Even though carbon dioxide deformation, etc. is disclosed, examples are limited to the reforming reaction of methanol and DME vapor.
U.S. Pat. No. 5,744,419 discloses a catalyst in which nickel or cobalt is carried in a support of silica, alumina, zirconia, etc. coated with an alkaline earth metal in advance according to the presence of a noble metal concerning a mixed reforming process of vapor reforming including oxygen reforming reaction and carbon dioxide reforming, and U.S. Pat. No. 4,026,823 discloses a nickel catalyst impregnating zirconia, where cobalt is added to nickel, as a vapor reforming catalyst of hydrocarbon.
As described above, studies on the noble metal catalyst and the decrease of catalyst life and activity due to carbon deposition are being actively conducted. However, the unit cost of the catalyst increases due to the use of expensive noble metals, and the replacement of the common nickel catalyst is impractical. Thus, studies on a monolith substrate maintaining activity thereof for a long time and economically useful are being actively conducted.
According to a literature to Soloviev, et al. [Journal of Natural Gas Chemistry, Carbon dioxide reforming of methane on monolithic Ni/Al2O3-based catalysts, 20 (2011), 184-190], a Ni/Al2O3-based catalyst is coated on a ceramic monolith, an alkali metal and rare earth metal are added thereto, and effects thereon is examined.
In U.S. Pat. No. 7,090,826, zirconia monolith coated with cerium oxide is prepared and applied to a partial oxidation process.
In Korean Patent Application No. 2009-0039582, a metal monolith catalyst for nature reforming is electrochemically formed using alumina and MgO and an enhancer of Ce, Ba and Sr. Korean Patent Application No. 2004-0118196 provides a vapor reforming structure catalyst in which a nickel-based catalyst is coated on a metal monolith.
As described above, studies on a monolith catalyst is being actively conducted, however studies on the activity of the monolith catalyst and the catalyst life with respect to a common catalyst are imperfect.
Accordingly, the present invention is completed by preparing a monolith catalyst that may replace a common nickel catalyst with low durability and stability, and by comparing with the common catalyst.